I have an older MiniBrew 7gal conical fermenter that I just resurrected. The top is just a rubber cap that stretches over the opening. Its tight but not airtight. Ive ran at least 10 brews through this unit with about 70% success. I've always thought that this can be a weak point for contaminants, but I shrugged it off as me just being too cautious. Would this concern anyone else?